Chemical Science. 187 



the substance to rise at temperature so low as 212,* without un- 

 dergoing any chemical change, except that the common crystals lose 

 two-thirds or two equivalents of their water of crystallization. If 

 ordinary oxalic acid be placed in a water bath, and heated, it efflo- 

 resces, losing nearly the proportion of water mentioned ; if exposed 

 to the cold air, it recovers the water ; but if continued hot, it sub- 

 limes, and minute acicular crystals form on the surface. If purified 

 oxalic acid in crystals be exposed to 350 or 400, in a deep evapo- 

 rating basin, and, when sublimation begins, the vessel be covered by 

 a layer of smooth filtering paper, a fold of blotting paper, and a 

 larger evaporating basin containing cold water, the oxalic acid con- 

 denses in crystals on the filtering paper, or falls on the side of the 

 dish, and after an hour may be removed, and quickly secured in a 

 stoppered bottle. Thus sublimed, the acid is in minute shining 

 acicular crystals, which, on exposure to air, become dull, and regain 

 the two equivalents of water. 



At higher temperatures the sublimation proceeds more rapidly. 

 At 300 or 330, none is decomposed f. At 360 or 400, the subli- 

 mation is very free ; at 414 it fuses, and boils freely ; above 330, 

 decomposition to a greater or smaller extent occurs, and is indicated 

 by the appearance of water. By combining the sublimed acid with 

 bases, &c. &c., its unchanged nature was ascertained. 



Dr. Turner found that a saturated solution of oxalic acid at the 

 temperature of 50, contained 1 part crystallized acid, and 15.5 

 parts water. At 57, 9.5 parts of water dissolved 1 part of crystal- 

 lized acid. At 212, the quantity of acid dissolved is almost unli- 

 mited ; at 220 the crystals fuse in the water of crystallization }. 



11. SCINTILLATION OF STEEL. INFLAMMATION OF GUNPOWDER. 



You inquire if we have ever tried whether gunpowder will fire in 

 the sparks from our polishing wheels . We have tried the experi- 

 ment, and find that when coarse emery is used on the wheels it will 

 be fired at any distance to which the sparks extend ; but when very 

 fine emery is used, a stream of innumerable sparks may be poured 

 upon coarse gunpowder without inflaming it. The same powder, 

 however, on being finely pulverized, will be readily inflamed by the 

 sparks from the fire wheel. In both cases, the sparks are particles 

 of ignited iron, and there can be no difference in the two cases, 



* It sublimes at common temperatures. See pp. 73, 74, of the last volume of this 

 Journal. 



f* See preceding page. 



J Phil. Mag., N. S. Jx. 161. 



The polishing wheels referred to are of various sizes and kinds, from large 

 grindstones, on which the gun-barrels are ground, to small wheels covered with 

 oiled leather and armed with emery powder. All these wheels are moved with 

 great rapidity by strong water power, and when the steel articles are held upon 

 them, there is a splendid coruscation of innumerable sparks flying off in tangent 

 lines, which follow oue another with such rapidity, that the wheel is constantly 

 surrounded with a glory. 



